The present invention relates generally to metallurgy, and more particularly to a method for metallurgically capping an end of a tube.
Resistance welding (also known as electric-resistance welding) is a known metallurgical process wherein metal is heated by its own resistance to a semi-fused (i.e., soft) or fused (i.e., molten) state by the passage of very heavy electric currents for very short lengths of time and then welded by the application of pressure.
Conventional methods for attaching parts together include gas metal arc welding. Gas metal arc welding uses a consumable metal wire as one electrode and the parts as another electrode, and moves the consumable metal wire (or the parts) to draw an arc and weld the parts together. The welding is accompanied by a gas (such as a mixture of argon and carbon dioxide) to prevent oxidation and stabilize the arc. Such gas metal arc welding is well known. In a conventional gas metal arc welding technique, solid metal wire or metal core wire (i.e., an annular-solid wire whose core is filled with metal powder such as a mixture of metal, alloy and/or oxide powders) is used with the wire at a positive electrical welding potential and with the parts electrically grounded. The welding arc creates a molten weld puddle which results in the welding together of the parts. A ceramic ferrule is used to contain the weld puddle when needed. Gas metal arc welding requires expensive welding equipment, the molten weld puddle tends to flow away from the joint area resulting in welds of inconsistent quality, and the process requires a long cycle time between welds.
Conventional methods for attaching parts together also include friction welding. To join two tubes together end to end, one of the tubes is rotated about its longitudinal axis, and the tube ends are pressed together, wherein friction causes heating of the ends creating the weld. To join a tube to a plate (such as an end cap plate), the tube is rotated about its longitudinal axis, and the tube end and the plate are pressed together, wherein friction causes heating creating the weld. Friction welding requires expensive welding equipment, and the process requires a long cycle time between welds.
What is needed is a less expensive method for metallurgically capping an end of a tube.
A first method of the invention is for metallurgically capping an end of a tube and includes steps a) through e). Step a) includes obtaining a tube having a tube end portion and having a passageway which extends to the tube end portion. Step b) includes obtaining a cap. Step c) includes, after steps a) and b), positioning the cap on the tube end portion covering the passageway. Step d) includes, after step c), folding the tube end portion of the tube around the cap creating an end portion fold while leaving a space within the fold. Step e) includes, after step d), creating a resistance welding current path through the tube and the cap proximate the fold and moving the fold deformingly against the cap creating a weld zone which includes at least some of the fold and at least some of the cap.
Several benefits and advantages are derived from one or more of the methods of the invention. Resistance welding is less expensive than gas metal arc welding or friction welding. Resistance welding also has a shorter cycle time between welds than gas metal arc welding or friction welding.